Mercury vapor lighting system



IN V EN TORS.

2 Sheets-Sheet 1 llll EWIIIF W. F. BLACKFORD El'AL MERCURY VAPOR LIGHTING SYSTEM Aug. 21,1956

Filed Feb. 16, 1 954 ZVaZZac'e 1. Black/am Jbseph C. Xaeyer fitter)? 2 Shets-Sheet 2 INVENTORS. Z/&Z Zace F'. .BZack/ara Joseph C. Yaeyer W. F. BLACKFORD ET AL MERCURY VAPOR LIGHTING SYSTEM Aug. 21, 1956 Filed Feb; 16, 1954 BY M 7 m an at tar/ 2g United States Patent G MERCURY VAPOR LIGHTING SYSTEM Wallace F. Blackford, Greendale, and Joseph C. Yaeger, Milwaukee, Wis., assignors to McGraw Electric Conn pany, Milwaukee, Wis, a corporation of Delaware Application February 16, 1954, Serial No. 410,684

12 Claims. (Cl. 315-422 This invention relates to a series system of mercury vapor lighting.

Until very recently, it has been the practice to connect an installation of mercury vapor lamps in parallel circuit relationship. In many instances it becomes desirable to connect these lamps in series relationship to gain the advantages of providing a single ballast for the lamps in the series loop, relatively low labor costs on initial installation, and other economic considerations. However, as in the case of series connected incandescent units, it becomes necessary to provide some means of maintaining continuity of service to the remaining lamps of a series loop should one lamp be extinguished and cause a break in the circuit. This invention contemplates the use of conventional film cutouts or other protective devices in shunt relationship with each lamp to continue the circuit onto the remaining lamps of the series loop should one or more of the lamps fail in service.

The use of film cutouts or the like introduces a problem peculiar to mercury vapor installations. That is, when the lamps are first started, there is a relatively high internal impedance, which is reduced considerably on ionization of the relatively low pressure atmosphere of the cool lamp. When the lamps are initially started, therefore, only a relatively safe voltage is required to strike or initiate the arc. During the normal operation of the lamps, the pressure within the lamp rises, but the arc is not interrupted as there is continuous ionization. However, when the circuit is interrupted, or if the supply voltage drops below that required to maintain ionization, the ionization will cease and the lamp will be extinguished. The pressure will remain high for several minutes after the lamp has been extinguished and until it has cooled down. The relatively high pressure makes it difficult to cause the gases to re-ioni'ze. In fact, the arc cannot be re-initiated until the lamp cools and the pressure is reduced sufiiciently to permit ionization. Any attempt to start the lamp or lamps will result merely in a destructive flashover. The film cutout provided in shunt relationship will be punctured if the circuit is opened and subsequently reclosed before the lamps have had time to cool down.

It, therefore, is an object of the present invention to provide an electrically driven time-delay system for series lighting of mercury vapor lamps in which each lamp is bridged or shunted by a film cut-out or other protective means that will puncture in the event of failure of a particular lamp, and which system Will provide a timedelay to permit series operated lamps to cool down sutficiently after an outage or drop in potential, thus protecting against the hazards of very high voltages and flash-over on restarting.

Series circuit mercury vapor systems have been provided in the past, but these systems have relied upon the use of thermally actuated devices such as bimetal elements operating against the action of electromagnetic hold-in coils which are in series connection with the lamps. Thus, when there was an outage or potential drop 2,760,115 Patented Aug. 21, 1956 that would influence the hold-in coil, the thermally actuated bimetal would urge contacts to a main oil switch to move to open position. The system would not permit restarting until the bimetal had cooled down and again close the contacts after a predetermined period of time. It will be apparent that devices using thermally actuated time-delay elements rely on a very large number of variables, and are materially alfected by ambient temperature changes. To compensate for ambient temperature changes merely adds the possibility of introducing another variable to the system. In addition, it has also been found, that in some cases, when there may be a direct break in the series loop to cause an outage, that there is the possibility of reenergizati'on of the circuit when the main contacts are again closed on cooling of the bimetallic element, this element being dependent upon a separate low potential pilot circuit. Such energization, even for 20 to 40 cycles would be sufficient to kill a lineman trying to repair the break.

It is therefore a specific object of the present invention to provide a series system for operation of mercury vapor lights, which includes the use of film cutouts for the individual lamps in the circuit, and which system provides an electrically driven time-delay means that is directly dependent upon drop in potential in the main supply circuit of sufficient magnitude to cause loss of ionization of lamps in the series circuit and which system will also protect where an open circuit may occur in the series circuit; and further, the operation of which may be actuated by a motor-operated cam device, or motoroperated spring return mechanism dependent only upon the measurement of drop in potential across fixed resistances.

It is a further object of the present invention to provide a series operated mercury vapor lighting system, which system includes the use of film cutouts, and which is relay controlled responsive to drop in potential of the source of supply and drop in current across the lamp circuit sufficient enough to extinguish the lamps, which introduces a time-delay for permitting restarting of the lamps by motor-driven cam means or motor-driven spring-return means, and which may be actuated either at the time the system is normally turned on, or at the time the system is turned off.

Embodiments of the invention are shown in the accompanying drawings in which:

Fig. 1 is a diagrammatic view of the motor-operated cam embodiment of the present invention.

Fig. 2 is a diagrammatic view of the motor-driven spring-return embodiment of this invention.

Referring now to Fig. 1, the preferred embodiment comprises a time-delay relay circuit indicated generally by the reference character 1 and the protective relay circuit indicated generally by the reference character 2. A remote control circuit interrupter, such as an oil switch 3, is provided for controlling the power supply to a constant current transformer or regulator 4, which may be of the static type, and thus to a series of mercury vapor lamps indicated at 5. The supply source is indicated generally at 6.

It will be apparent that the protective relay 2 may be directly embodied in the structure of the transformer 4, being dependent on internal well-known characteristics of such regulators responsive to open circuit conditions on the regulated side.

Each of the mercury vapor lamps 5 is bridged or shunted by means of a. film cut-out or other protective device, indicated generally by the reference character 7. The film cut-out has a sufiiciently high break-down voltage to withstand a voltage which is an excess of the starting voltage of the individual lamp across which it is bridged, but generally not sufiicient to withstand the full value of the voltage across series loop. However, in the case of a single lamp, the cutout will necessarily be selected to withstand normal applied voltage in its individual circuit. The time-delay relay circuit may be supplied with low-voltage suitable for the electrical characteristics of the various relay circuit components by means of a potential transformer 8 having its primary coil supplied from the high-voltage circuit 6. The operation of the relay circuit, and consequently the lamp circuit, is controlled by a main control switch 9. It is the general practice to actuate the main control switch by means of a time clock control, photoelectric control, or pilot wire relay (not shown) in the case of street lighting.

The circuit interrupter or switch 3 comprises the movable contacts 10 which are normally biased open. The contacts are closed when the operating coil 11 is energized, thereby drawing the plunger 12 upwardly and closing the circuit to the lamps through the constant current transformer, or regulator 4.

The time-delay relay circuit 1 is preferably grounded as shown and protected by means of a conventional lightning arrester 13. The circuit comprises an undirectional motor 15, a time-delay cam 16, and two relays denoted generally by the reference characters 17 and 18.

The time-delay cam 16 is preferably operated in a clockwise direction as shown in Fig. 1 by the motor 15. Operation of the motor takes place in two sequences, which are established by operation of the relays 17 and 18, as will hereinafter be described.

The normally closed contacts 19 of the switch 20 are biased towards closure and are urged towards open position as the cam follower 21 rides on the high timedelay surface of the rotating cam 16. The follower normally rests, as shown, in the indent 22 of the cam. The switch 20 also includes a pair of normally open contacts 23 which are closed on rotational operation of the cam 16 simultaneously with the opening action of contacts 19.

Referring again to the relay 17, the operating coil 24, when energized, operates to draw the plunger 25 upwardly to close the normally open contacts 26 and 27. The relay 17 initially controls the operation of the relay 18, which includes a voltage responsive operating coil 30, the resistance of which when taken in conjunction with the resistance of the resistor 31, measures the potential of the secondary of the potential transformer 8. Coil 30 of relay 18, when energized, operates to draw the plunger 32 upwardly to close the normally open contacts 33 and 34, and to open the normally closed contact 35.

Contacts 26 of relay 17, when closed, complete the circuit through the coil 30 of relay 18, while contacts 27 of that relay, when closed, complete the circuit to the motor 15.

Normally closed contacts 35 of relay 18 act to establish a circuit to the motor 15 through the contacts 23 of switch 24 when in closed position, as will hereinafter be described. Normally open contacts 34, when closed, adds the resistance 31 in the circuit with the coil 30 to make the relay 18 drop out if the impressed voltage drops to or below a predetermined value. Contacts 33 of relay 18, when closed, complete the circuit through the protective relay 2.

Referring now to protective relay 2, this relay has two switch elements, or means, indicated at and 41. As shown with the control switch 2 in open position, both switch means 46 and 41 are normally closed. The switch 40 is held open whenever the magnet coil 42 is energized, such coil being connected in the series loop of the mercury vapor lamps 5. The switch 40 controls the energization of the magnet coil 43, which, in turn, controls the switch 41. Whenever the coil 43 is energized, the switch 41 is urged to move in a direction against a timedelay means, such as dashpot 44. It will be seen, therefore, with reference to Fig. 1, that normally the switches 4 40 and 41 are closed. When the control switch 9 closed, and after the components of circuit 1 have operated, the coil 43 is momentarily energized. As soon as the current flows and lamps 5 light, the coil 42 will be energized and the circuit to the coil 43 will be broken before the switch 41 can be opened. It has been found that a delay of 20 to 40 cycles by means of the dashpot 4-4 is sufficient to cause the coil 43 to become dcenergizcd before contacts 41 can be opened.

The operation of the apparatus is as follows:

Assuming the control switch 9 to be in open position, as shown in Fig. l with the lights being turned off, it will be noted that contacts 19 on switch 20 are in closed position and contacts 23 are in open position.

To operate the lamps 5, the control switch 9 is closed either manually, or by some means such as a photoelectric cell or time clock. The circuit from the switch 9 is now established through the operating coil 24 of the relay 17 to the normally closed contacts 19 of switch 21) and back through the secondary winding of the potential transformer 8. The relay 17 will then operate to draw the plunger 25 upwardly and close contacts 26 and 27. The closure of contacts 26 will complete the circuit through the coil 30 of relay 18, and cause the plunger 32 to be drawn upwardly to simultaneously close contacts 33 and 34 and open contacts 35. It is now to be noted that closure of contacts 34 also completes a parallel electrical circuit through the relays own operating coil 30 and resistor 31 to the secondary of the transformer 8.

Closure of contacts 27 of relay 17 completes the circuit to the motor 15 which causes immediate rotation of the cam 16. The cam follower 21 will then be caused to rise from the indent 22 to the high time-delay surface of the cam 16, to simultaneously open contacts 19 and close contacts 23. The opening of contacts 19 will immediately drop out coil 24 of relay 17. It will be obvious that When coil 24 is dropped out of circuit. the contacts 27 will be opened, and the motor will be immediately caused to stop with the cam follower 21 resting on the high surface of cam 16 (not shown).

Relay 18 remains held in through its own closed contacts 34, and the resistor 31. The combination of resistor 31 and coil 30 is such that if the impressed voltage is insufiicient, the relay will immediately drop to its deenergized position. The closure of contacts 33 of relay 18 completes the circuit from the potential transformer 8 through coil 30 of relay 1, through the normally closed switch means 41 of relay 2, and thus to the coil 11 of the circuit interrupter 3. Energization of coil 11 causes the plunger 12 to be drawn upwardly and close the movable contacts 10 and complete the supply circuit to the constant current transformer or regulator 4 to the mercury vapor lamps 5, and through the coil 42 of the protective relay 2 after the lamps are lit. Energization of coil 42 will cause the switch 40 to be opened and thus de-energize coil 43 permitting switch 41 to remain closed to allow the interrupter 3 to remain energized.

On the occurrence of a drop in potential in the supply circuit 6, the time delay relay will operate as follows:

If the voltage should drop below a predetermined value, the arc would not be supported between the electrodes of the lamp and would consequently require a restarting operation when the voltage supply is again restored. Obviously, if the lamps have not cooled sufficiently, the pressure would be very high and the increased voltage would result merely in a destructive flash-over which would puncture the film cut-out.

Any drop in potential in the supply circuit 6 is immediately reflected in the secondary of the potential transformer 8, and consequently through the operating coil 30 of relay 18 and its resistor 31 through the contacts 34. The drop in voltage will therefore permit the release of the upwardly held plunger 32 causing the con tacts 33 and 34 to be opened and contacts to be closed. It will be remembered that when the control switch 9 was originally closed, the cam follower 21 was subsequently caused to rise to the time-delay surface of the cam 16. Contacts 19 were then moved to open position and the contacts 23 were simultaneously closed.

Closure of contacts 35 completes the circuit through contacts 23 to immediately energize the motor 15. Operation of the motor will cause the cam to rotate and provide a predetermined time-delay before the cam follower 21 will be caused to rest in the indent portion of the cam. When the cam follower 21 rests in the indent portion, the contacts 23 will immediately open and cause the motor to stop operating. The cycle of operation is now ready to begin once again.

However, during the time-delay period and substantially simultaneously with the energization of the motor, the circuit to the protective relay 2 is broken when the contacts 33 are opened. This will de-energize the holding coil 11 of the interrupter 3 to release the plunger 12 to open the movable circuit contacts 1i) and interrupt the supply to the transformer 4, and thus de-energize the lamps 5 until they have cooled down sufficiently to permit restriking of the are without destructure flashover.

When the supply to the transformer 4 from the source 6 has been opened, the coil 42 of the protective relay will be tie-energized and permit the switch 46 to be closed and complete the circuit to the coil 43.

On the occurrence of an open circuit fault in the series loop, the switch 49 will be caused to close by the deenergization of the coil 42. Closure of switch 49 will energize the coil 43, provided that potential is available from the relay circuit 1. This will draw the plunger upwardly to open the switch 41, and thus interrupt the circult to the circuit interrupter 3.

On normal operation of the control switch 9 to open position, the coil 3h will permit the plunger 32 to drop downwardly and close the contacts 35 with a simultaneous opening operation of contacts 33 and 34. Opening of contacts 33 will interrupt the circuit to the protective relay 2, and consequently release the plunger 12 of the circuit interrupter 3 to tie-energize the circuit to the regulator t supplying the lamps. It is to be noted, however, that the control switch 9 has been placed in the circuit following the motor 15, to permit the operation of the motor and initiate a time-delay period after the lights have been turned off. This is desirable, in that if the switch had been placed intermediate the motor and the potential transformer 8, a timedelay would be introduced immediately after the switch is moved to on position and the lights would not be lit for the period of the time-delay, even when they are cool and ready for operation.

The second embodiment of this invention is shown diagrammatically in Fig. 2 and. includes the use of a motor-operated spring-return mechanism in combination with a motor, which inherently provides a predetermined time-delay. inasmuch as a goo-d share of Fig. 2 shows substantially the same construction as that previously described in connection with Fig. 1, the same reference characters will be used wherever possible to indicate the same parts.

-he main difference between the embodiments of Fig. l and Fig. 2 is in the components of the timedelay circuit, which was generally denoted in Fig. l by the reference numeral ii. The time-delay circuit of Fig. 2 is generally denoted by the reference character 60, and comprises a motor 61 having a spring-return means 62 incorporated therein. The motor also incorporates a gear train or similar means for providing a measured speed of rotation in operation (not shown). An example of a suitable, small, self-starting synchronous motor, which may be used for operation in the relay circuit 60, is illustrated in the patent of E. L. Schellens, No. 2,334,040, filed November 9, 1943.

Cit

In addition to the motor 61, three relays are provided and are generally denoted by the reference characters 63, 64 and 65, respectively. As shown in Fig. 2, with the main control switch 9 in open position, the relay 63 comprises an operating coil 70, a plunger 71 adapted to be drawn towards closure of the normally open contacts 72 on energization of coil 70. A resistor 73 is positioned for series relationship with the coil to provide a predetermined resistance which will close the contacts 72 when the supply is above a predetermined norm, and which will permit the contacts to open if the control voltage is less than that norm. Initial operation of the motor 61 is controlled by closure of the contacts 72 of relay 63. The motor 61 operates the switch 74 to close the normally open switch contacts 75.

Relay 64 comprises an operating coil 80, which is energized on closure of the contacts of the switch 74. The operating coil of relay 64, when energized, operates to draw the plunger 81 towards closure of the normally open contacts 82 and 83, respectively. Contacts 82 are so connected with contacts 83 to act as a circuit holding means for the relay 64 during normal operation of the device.

Relay 65 comprises an operating coil 90, which, when energized, operates to draw the plunger 91 upwardly to open the normally closed contacts 92 and 93, respectively. As shown, the normally closed contacts 92 act to provide a short-circuit path around the resistor 73, and contacts 93 complete the circuit through the motor to permit instantaneous operation of the motor when contacts 72 of relay 63 are brought to closed position. Opening operation of contacts 93 also prevents stalling of motor 61, and permits the spring mechanism to return to normal position on energization of coil of relay 65.

Operation of the embodiment of Fig. 2 is as follows:

Assuming the control switch 9 to be in open position, as shown in Fig. 2, with the lights being turned off, it will be noted that the motor 61 is immediately available for operation as soon as contacts 72 of relay 63 are closed.

To operate the lamps 5, the control switch 9 is closed either manually, or by conventional means, such as a photo-electric relay, pilot wire relay, or time clock. The circuit from the switch 9 will be established through the coil 70 of relay 63 and the normally closed contacts 92 of relay 65 to the secondary of the potential transformer 8. Energization of the coil 70 causes the plunger 71 to be drawn inwardly to close the normally open contacts 72 and start the motor 61 in its operation. In the embodiment of Fig. 2, it is to be noted that the motor goes through its entire time-delay cycle before closure of the contacts 75, as contrasted with the motor-operated cam 16 of the embodiment of Fig. 1, which provides the timedelay previous to the restoration of energy to the lamp circuit. It is usually deemed preferable to have the lamps instantaneously available for lighting when the control switch is closed, rather than to wait for the time delay period to expire. However, the embodiment of Fig. 2 operates very effectively for the protection of the circuit, which is the main function of the invention.

After the motor has rotated through its time-delay cycle, the switch 74 is moved to close its contacts 75 and complete the circuit through the coil 80 of relay 64. This immediately causes the plunger 81 to be drawn downwardly and close the normally open contacts 82 and 83.

Closure of contacts 82 provides a holding circuit through the coil 80 to prevent de-energization thereof.

Closure of contacts 83 completes the circuit through the coil 90 of relay 65 to draw the armature 91 upwardly into the coil and open the contacts 92 and 93. Opening of contacts 93 completely de-energizes the circuit to the motor 61, and opening of contacts 92 connects the resistor 73 in series with coil 70 to make the relay 63 drop out if the impressed voltage drops to or below a predetermined value. After the motor has operated through its time-delay perior to close the contacts 75, the integral spring-return mechanism 62 causes an axial shift of the motor armature (not shown) to permit the motor to reset itself and simultaneously open the contacts 75 to be available for further operation if needed.

Closure of the contacts 83 of relay 64 also completes the circuit from the previously closed contacts 72 of relay 63 to the protective relay 2, the operation of which has previously been described in connection with Fig. l. The circuit is now established through the switch 41 of protective relay 2 to the operating coil 11 of the interrupter 3 to cause the movable contacts 19 to be closed and complete the circuit to the constant current transformer 4, and thus to the series-connected mercury vapor lamps 5 and the operating coil 42 of the relay 2. The lamps will now become energized and after being lit. will cause the coil 42 to permit the switch 4-0 to open and de-energize the coil 43, and thereby prevent it from opening the switch contacts 41.

On the occurrence of a drop in potential, as reflected in the secondary of potential transformer 8 and thus to the time-delay circuit 60, the combined resistances of the coil 70 of relay 63 and the resistor 73 will permit release of the plunger 70 and opening of the contacts 72. Opening of the contacts 72 will interrupt the circuit through the contacts 82 of the relay 64 and consequently de-energize the operating coil 80 of the relay 64 to permit the contacts 83 to be opened and interrupt the circuit to the protective relay 2 and to the coil 90 of relay 65. The contacts 92 and 93 of relay 65 will be returned to the position shown in Fig. 2, and complete the circuit to the motor 61 and cut out the resistor 73. Opening of the contacts 83 of relay 64 interrupts the circuit through the switch contacts 41 of relay 2 to the operating coil 11 of the interrupter 3 to permit the movable contacts 10 of the interrupter to be moved to open position.

Restoration of the normal voltage will cause the timedelay circuit to be re-established, as described above, and relight the lamps 5. However, coil 63 itself, is voltage sensitive and will not actuate plunger 71 until the control voltage has been restored to a predetermined value.

An open circuit condition in the lamp circuit will cause the operation of the protective relay 2 substantially as described in connection with the embodiment of Fig. 1.

When it is desired to turn off the light either manually or by means of a photoelectric cell or time clock, the control switch 9 is actuated to open position and cause immediate release of the coil 70 of relay 63 to open contacts 72. The interconnected contacts 83 and 82 of relay 64 will now be opened by interruption of the circuit through the holding contacts 82. Opening of contacts 83 will interrupt the circuit to the protective relay and consequently de-energize the operating coil 11 of the circuit interrupters 3 to move the contacts 10 to open position.

It is intended that the use of the term electrically driven time delay" throughout the specification and claims be considered in its broad sense to include a spring driven, electrically wound device that permits initiation of a timedelay even on complete de-energization of the supply circuit.

It will be seen that a very simple type of electrically driven time-delay relay circuit has been provided which is eminently suited for use with mercury vapor lamps arranged in a series system. Also, it is to be noted particularly that the switch is so arranged that it can be used in such a system where film cut-outs are provided in shunt with each of the mercury vapor lamps without any danger of puncturing the film in the normal operation of starting and stopping the system.

We claim:

1. A protective electrical relay circuit for a series system of mercury vapor lighting comprising a plurality of series connected lamps, a cut-out shunted across each lamp for shorting out any lamp upon failure thereof, a substantially constant current source, and a circuit interrupter for energization of said lamps; said relay circuit comprising voltage sensitive means energized from said source for controlling said interrupter, said means being adapted to release said interrupter when the voltage of said source falls below a predetermined magnitude, and electrically driven time delay means for preventing reclosure of said interrupter for a predetermined interval greater than that required for cooling of the lamps after said lamps have been extinguished, each cut-out being characterized by the fact that it will short circuit its corresponding lamp for voltages less than that required to restart the lamp when the lamp is hot.

2. A protective electrical relay circuit for a series system of mercury vapor lighting comprising a plurality of series connected lamps, a cut-out shunted across each lamp for shorting out any lamp upon failure thereof, a substantially constant current source, and a circuit interrupter for energization of said lamps; said relay circuit comprising voltage sensitive means energized from said source for controlling said interrupter, said means being adapted to release said interrupter when the voltage of said source falls below a predetermined magnitude, electrically driven time delay means for preventing reclosure of said interrupter for a predetermined interval greater than that required for cooling of the lamps after said lamps have been extinguished, and means actuated upon the operation of said voltage sensitive means for subsequently inserting a resistance in the energizing circuit to said voltage sensitive means, each cut-out being characterized by the fact that it will short circuit its corresponding lamp for voltages less than that required to restart the lamp when the lamp is hot.

3. A protective electrical relay circuit for a series system of mercury vapor lighting comprising a plurality of series connected lamps, a cut-out shunted across each lamp for shorting out any lamp upon failure thereof, a substantially constant current source, and a circuit interrupter for energization of said lamps; said relay circuit comprising voltage sensitive means energized from said source for controlling said interrupter, said means being adapted to release said interrupter when the voltage of said source falls below a predetermined magnitude, electrically driven time delay means for preventing reclosure of said interrupter for a predetermined interval greater than that required for cooling of the lamps after said lamps have been extinguished, means actuated upon the operation of said voltage sensitive means for subsequently inserting a resistance in the energizing circuit to said voltage sensitive means, and relay means concurrently controlling said interrupter with said voltage sensitive means and including an operating coil in series circuit with said lamps and adapted to release sad interrupter on the occurrence of an open circuit fault in said lamp circuit, each cut-out being characterized by the fact that it will short circuit its corresponding lamp for voltages less than that required to restart the lamp when the lamp is hot.

4. A protective electrical relay circuit for a series system of mercury vapor lighting comprising a plurality of series connected lamps, a cut-out shunted across each lamp for shorting out any lamp upon failure thereof, a substantially constant current source, and a circuit interrupter for energization of said lamps; said relay circuit comprising voltage sensitive means energized from said source for controlling said interrupter, electrically driven time delay means for controlling said voltage sensitive means, said voltage sensitive means, when energized, being adapted to hold said interrupter closed and also being adapted to release said interrupter and to energize said time delay means when the voltage of said source falls below a predetermined value, said time delay means adapted to alternatively control the closure of the circuit to said voltage sensitive device for normal operation of said lamps and to open the circuit to said voltage sensitive device for preventing reclosure of said interrupter for a predetermined delay period greater than that required for 9 cooling of the lamps immediately following opening of said interrupter, each cut-out being characterized by the fact that it will short circuit its corresponding lamp for voltages less than that required to restart the lamp when the lamp is hot.

5. A protective electrical relay circuit for a series system of mercury vapor lighting comprising a plurality of series connected lamps, a cut-out shunted across each lamp for shorting out any lamp upon failure thereof, a substantially constant current source, and a circuit interrupter for energization of said lamps; said relay circuit comprising voltage sensitive means energized from said source for controlling said interrupter, electrically driven time delay means for controlling said voltage sensitive means, said voltage sensitive means, when energized, being adapted to hold said interrupter closed and also being adapted to release said interrupter and to energize said time delay means when the voltage of said source falls below a predetermined value, said time delay means adapted to alternatively close the circuit to said voltage sensitive device for normal operation of said lamps and to open the circuit to said voltage sensitive device for preventing reclosure of said interrupter for a predetermined delay period greater than that required for cooling of the lamps immediately following opening of said interrupter, and relay means concurrently controlling said interrupter with said voltage sensitive means and including an operating coil in series circuit with said lamps and adapted to release said interrupter on the occurrence of an open circuit fault in said lamp circuit, each cut-out being characterized by the fact that it will short circuit its corresponding lamp for voltages less than that required to restart the lamp when the lamp is hot.

6. A protective electrical relay circuit for a series system of mercury vapor lighting comprising a plurality of series connected lamps, a cut-out shunted across each lamp for shorting out any lamp upon failure thereof, a substantially constant current source, and a circuit interrupter for energization of said lamps; said relay circuit comprising voltage sensitive means energized from said source for controlling said interrupter, motor-driven cam means for controlling said volt-age sensitive means, said voltage sensitive means, when energized, being adapted to hold said interrupter closed and also being adapted to release said interrupter and to energize said cam means when the voltage of said source falls below a predetermined value, said cam means providing a time delay interval adapted to alternatively close the circuit to said voltage sensitive device for normal operation of said lamps and to open the circuit to said voltage sensitive device for preventing reclosure of said interrupter for a predetermined delay period greater than that required for cooling of the lamps immediately following opening of said interrupter, each cut-out being characterized by the fact that it will short circuit its corresponding lamp for voltages less than that required to restart the lamp when the lamp is hot.

7. A protective electrical relay circuit for a series system of mercury vapor lighting comprising a plurality of series connected lamps, a cut-out shunted across each lamp for shorting out any lamp upon failure thereof, a substantially constant current source, and a circuit interrupter for energization of said lamps; said relay circuit comprising voltage sensitive means energized from said source for controlling said interrupter, electrically driven time delay means for controlling said voltage sensitive means, said voltage sensitive means, when energized, being adapted to hold said interrupter closed after the expiration of a predetermined time delay interval, and also being adapted to release said interrupter when the voltage of said source falls below a predetermined value, said time delay means adapted to close the circuit to said voltage sensitive device for normal operation of said lamps after the lapse of said time delay interval, said time delay 10 interval being longer than the cooling period of the lamps, each cut-out being characterized by the fact that it will short circuit its corresponding lamp for voltages less than that required to restart the lamp when the lamp is hot.

8. A protective electrical relay circuit for a series sys tem of mercury vapor lighting comprising a plurality of series connected lamp-s, a cut-out shunted across each lamp for shorting out any lamp upon failure thereof, a substantially constant current source, and a circuit interrupter for energization of said lamps; said relay circuit comprising voltage sensitive means energized from said source for controlling said interrupter, electrically driven time-delay means for controlling said voltage sensitive means, said voltage sensitive means, when energized, being adapted to hold said interrupter closed after the expiration of a predetermined time delay interval, and also being adapted to release said interrupter when the voltage of said source falls below a predetermined value, said time delay means adapted to close the circuit to said voltage sensitive device for normal operation of a lamp after the lapse of said time delay interval greater than the cooling period of the lamps, and relay means concurrently controlling said interrupter with said voltage sensitive means and including an operating coil in series circuit with said lamps and adapted to release said interrupter on the occurrence of an open circuit fault in said lamp circuit, each cut-out being characterized by the fact that it will short circuit its corresponding lamp for voltages less than that required to restart the lamp when the lamp is hot.

9. A protective electrical relay circuit for a series system of mercury vapor lighting comprising a plurality of series connected lamps, a cut-out shunted across each lamp for shorting out any lamp upon failure thereof, a substantially constant current source, and a circuit interrupter for energization of said lamps; said relay circuit comprising voltage sensitive means energized from said source for controlling said interrupter, time delay means consisting of an electric spring-return motor for controlling said voltage sensitive means, said voltage sensitive means, when energized, being adapted to hold said interrupter closed after the expiration of a predetermined time delay interval, and being adapted to release said interrupter when the voltage of said source falls below a predetermined value, said spring-return motor adapted to close the circuit to said voltage sensitive device for normal operation of said lamps after the lapse of a time delay interval greater than the cooling period of the lamps, each cut-out being characterized by the fact that it will short circuit its corresponding lamp for voltages less than that required to restart the lamp when the lamp is hot.

10. In a series system of mercury vapor lighting a plurality of lamps connected in a series circuit, a source of substantially constant current for said circuit, a main circuit interrupter controlling the connection between said series circuit and said source, a cut-out shunted across each lamp, each cut-out being characterized by the fact that it will short circuit its individual lamp for voltages below that required to cause restriking of the lamp when the lamp is hot, a main control switch operatively controlling the opening and closing of said main circuit interrupter, and electrically driven time delay means for delaying the closing of said main circuit interrupter after said main circuit interrupter has been opened, the delay of said time delay means being greater than the cooling period of said lamps whereby shorting of any of said lamps by its cut-out is prevented on reclosing of said main circuit interrupter.

11. In a series system of mercury vapor lighting a plurality of lamps connected in a series circuit, a source of substantially constant current for said circuit, a main circuit interrupted controlling the connection between said series circuit and said source, a cut-out shunted across each lamp, each cut-out being characterized by the fact that it will short circuit its individual lamp for voltages below that required to cause restriking of the lamp when the lamp is hot, a main control switch operatively controlling the opening and closing of said main circuit interrupter, and electrically driven time delay means for delaying the closing of said main circuit interrupter after said main circuit interrupter has been opened, said time delay means inter-posing its delay period while said lamps are extinguished, the delay of said time delay means being greater than the cooling period of said lamps whereby shorting of any of said lamps by its cut-out is prevented on reclosing of said main circuit interrupter.

12. In a series system of mercury vapor lighting a plurality of lamps connected in a series circuit, a source of substantially constant current for said circuit, a main circuit interrupter controlling the connection between said series circuit and said source, a cut-out shunted across each lamp, each cut-out being characterized by the fact that it will short circuit its individual lamp for voltages below that required to cause restriking of the lamp when the lamp is hot, :1 main control switch operatively controlling the opening and closing of said main circuit interrupter, and electrically driven time delay means for delaying the closing of said main circuit interrupter after said main circuit interrupter has been opened, said time delay means interposing its delay period after said main control switch has been closed, the delay of said time delay means being greater than the cooling period of said lamps whereby shorting of any of said lamps by its cut-out is prevented on reclosing of said main circuit interrupte References Cited in the file of this patent UNITED STATES PATENTS 2,018,256 Ellett Oct. 22, 1935 2,068,621 Lemmon Jan. 19, 1937 2,106,211 Guin Jan. 25, 1938 2,479,179 Newbill Aug. 16, 1949 

